WASHINGTON — Scott Pruitt, the Environmental Protection Agency administrator, insisted on staying in luxury hotels that were costlier than allowed by government standards, while also pushing to fly on an airline not on the government’s approved list so he could accrue more frequent flier miles, one of his top former deputies at agency has told congressional investigators.

In a separate letter on Thursday, Democratic lawmakers also demanded information about two previously unknown E.P.A. email addresses that have been used by Mr. Pruitt, asking if they were a tool for withholding public information from records requests. Their letter echoes a controversy in 2012, during the Obama administration, when Lisa P. Jackson, who was E.P.A. chief at the time, was criticized for a similar use of an undisclosed E.P.A. email account.

Jahan Wilcox, a spokesman for the E.P.A., said the agency had consistently searched all email addresses associated with Mr. Pruitt when responding to records requests. Of the allegations outlined to lawmakers by Mr. Chmielewski, he said, “We will respond to members of Congress through the proper channel.”

Ms. Jackson, who was President Obama’s first E.P.A. administrator, came under fire from Republican lawmakers when it was found that she used a secondary E.P.A. email address, under the name “Richard Windsor,” for government correspondence. The name was a combination of Ms. Jackson’s family dog growing up and her hometown, East Windsor Township, in New Jersey.

According to Thursday’s six-page letter from lawmakers, Mr. Chmielewski told congressional staff members during a meeting this week that Mr. Pruitt would often seek to schedule trips back to Oklahoma, where he still owns a home, so he could stay there for weekends. “Find me something to do,” were the instructions Mr. Pruitt gave his staff, after telling them he wanted to travel to particular destinations, the letter says, quoting Mr. Chmielewski, who was expected to sign off on the trips.

When planning a trip to Italy, Mr. Pruitt “refused to stay at hotels recommended by the U.S. Embassy, although the recommended hotel had law enforcement and other U.S. resources on site,” according to the letter, which was written and sent to Mr. Pruitt, asking him to turn over documents related to the letter’s claims. Instead, Mr. Pruitt chose to stay “at more expensive hotels with fewer standard security resources,” while bringing along his own security team “at taxpayer expense.”

For other trips, Mr. Pruitt pushed the agency to book him on Delta, even though it is not the federal government’s contract carrier, “because you want to accrue more frequent flier miles,” the letter says.

The letter says that while Mr. Pruitt was living last year in a Capitol Hill condominium rented from the wife of an energy lobbyist, complaints came in to the E.P.A. from the lobbyist, J. Steven Hart, that “you had never paid any rent to him, and that your daughter damaged his hardwood floors by repeatedly rolling her luggage across the unit when she was staying there.”

A spokesman for Mr. Hart challenged the assertions in the letters from the Democrats, saying that his wife, Vicki, was the only one who had contacted the E.P.A. and that the hardwood floors were not damaged. The spokesman added that Mr. Pruitt ultimately paid the rent, though he paid late.

Mr. Chmielewski also provided details about how Mr. Pruitt had assigned one of his aides, Millan Hupp, to “act as your personal real estate representative, spending weeks improperly using federal government resources and time to contact rental and seller’s agents, and touring numerous properties in which you might wish to reside.”

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Kevin Chmielewksi at the lectern at a Trump rally in Berlin, Md., in 2016.CreditStewart Dobson/Ocean City Today

The letter also corroborates details previously reported by The New York Times, including that Mr. Pruitt and others at the agency retaliated against staff members, including Mr. Chmielewski, when they objected to the spending requests.

Mr. Chmielewski, for example, refused to approve first-class travel for one of Mr. Pruitt’s aides for a trip Mr. Pruitt took to Morocco last year, saying the cost violated federal rules. After that, he was told by Mr. Pruitt’s chief of staff, Ryan Jackson, that he was going to be fired or reassigned.

“The new information provided by Mr. Chmielewski, if accurate, leaves us certain that your leadership at E.P.A. has been fraught with numerous and repeated unethical and potentially illegal actions on a wide range of consequential matters,” the letter says. It was signed by Representatives Elijah Cummings of Maryland, Gerald E. Connolly of Virginia and Donald S. Beyer Jr. of Virginia, as well as Senators Sheldon Whitehouse of Rhode Island and Thomas R. Carper of Delaware.

According to the letter, Mr. Chmielewski also told the lawmakers that for “a period of weeks” he did not see Samantha Dravis, Mr. Pruitt’s policy chief, at work. Mr. Carper had previously asked the inspector general to investigate Ms. Dravis’ work attendance, saying her alleged absence during much of November, December and January “raises questions” about whether the agency is adhering to internal rules regarding employee time and attendance.

On Monday the inspector general’s office agreed to investigate the matter.

Ms. Dravis said in a statement last week that she had never been absent from work for weeks at a time and that she performed her duties “tirelessly and diligently” for her entire tenure.

Mr. Chmielewski also told lawmakers that Mr. Pruitt had provided approval for Ms. Dravis to fly first class on the administrator’s 2017 trip to Morocco, “even though there was no legal justification for her to do so.” He contended that Ms. Dravis and Ms. Hupp asked him to retroactively sign paperwork after the trip to justify the decision, which he said he refused to do.

On Thursday, a person familiar with Ms. Dravis’s defense regarding the flight disputed the allegation, saying that Ms. Dravis had been upgraded to business class on one leg of the return flight from Morocco and that the upgrade had been authorized before the trip. Federal agency policy forbids premium-class travel but makes exceptions in certain circumstances, for instance on flights longer than 14 hours.

In a letter to the E.P.A. inspector general on Thursday, Mr. Carper and Senator Jeff Merkley, Democrat of Oregon, said they would like to know if public information had been withheld from public-records requests through the use of the two additional email addresses by Mr. Pruitt.

“We write to share our deep concern over Administrator Pruitt’s reported use of multiple email accounts,” Mr. Merkley and Mr. Carper wrote. “It is imperative that there be an investigation into whether the agency has properly searched these email addresses for responsive documents in response to Freedom of Information Act (FOIA) requests.”

Lawmakers had previously been aware of two email address for Mr. Pruitt: his main address, pruitt.scott@epa.gov, to which the public could send correspondence; and adm14pruitt@epa.gov, which was used for administrative purposes, for instance scheduling. Congressional aides said they recently learned of two new addresses: esp7@epa.gov and sooners7@epa.gov, named for the Oklahoma Sooners football team.

The existence of the previously undisclosed email address was reported by the Washington Post. Four E.P.A. officials independently confirmed the addresses as being used by the administrator and his staff.

Asked for comment on the additional email addresses, Jahan Wilcox, an E.P.A. spokesman, said: “When E.P.A. receives a FOIA request concerning the administrator’s emails, all accounts associated are searched before we respond to that request.”

A few hours later, Mr. Wilcox said in a separate statement that the agency maintained three email addresses attributed to Mr. Pruitt, two of which are used by the staff to coordinate his calendar and public correspondence, with the third used by the administrator himself. “A fourth email account was created for use by the administrator but was superseded and never used beyond three test emails,” Mr. Wilcox said. He did not specify which accounts were used for which purposes.